Secondary batteries such as lithium ion secondary batteries and nickel metal-hydride secondary batteries are, nowadays, widely used as driving power sources for portable electronic devices such as mobile telephones, portable personal computers, and portable music players or as power sources for hybrid electric vehicles (HEVs and PHEVs), and electric vehicles (EVs).
These secondary batteries are more desired to have a square form than a cylindrical form particularly when space efficiency is demanded. Moreover, a metal case is generally used as the outer body of a battery when physical strength is required.
A prismatic sealed secondary battery, for example, a prismatic nonaqueous electrolyte secondary battery is manufactured in the following manner. Specifically, a negative active material compound containing a negative active material is applied to each surface of a negative electrode substrate (current collector) made of a narrow sheet-like copper foil to manufacture a negative electrode plate. Also, a positive active material compound containing a positive active material is applied to each surface of a positive electrode substrate (current collector) made of a narrow sheet-like aluminum foil to manufacture a positive electrode plate.
Then, the negative electrode plate and the positive electrode plate are laminated on each other by interposing a separator made of, for example, a microporous polyethylene film between the both and spirally wound around a cylindrical winding core in the condition that the negative electrode plate and the positive electrode plate are insulated from each other to manufacture a cylindrical winding electrode assembly.
Then, this cylindrical winding electrode assembly is pressed by a press machine to form the electrode into such a flat winding electrode assembly that the electrode assembly can be inserted into a prismatic battery outer body and then, accommodated in the prismatic outer body. Then, an opening except for an electrolyte pour hole in the battery outer body is closed, an electrolyte is injected into the outer body, and finally, the electrolyte pour hole is closed to make a prismatic nonaqueous electrolyte secondary battery.
When a metal case is adopted as the outer body, the electrode is accommodated in a metal case (hereinafter referred to as “outer can”) which is an outer body after the above flat winding electrode assembly is wrapped with an insulation member for insulating the electrode from the case to thereby manufacture a prismatic nonaqueous electrolyte secondary battery.
As an example of a prismatic secondary battery in which a flat winding electrode assembly is accommodated in an outer can in the condition that it is wrapped with an insulation member, the following Patent Literature 1 discloses an invention of a prismatic battery most suitable for EV or HEV use because it is resistant to damages to the surface of a flat electrode assembly in the process of inserting the electrode into a prismatic metal outer can in the production of the battery and can be also charged/discharged under a large current though the positive electrode plate and negative electrode plate are electrically insulated from the prismatic metal battery outer can.
In a conventional prismatic secondary battery as disclosed in the following Patent Literature 1, the insulation sheet is cut into a predetermined shape, then, folded and formed into a predetermined form (hereinafter, the insulation sheet formed into a predetermined form is referred to as “box-shaped insulation sheet”) and usually into a cuboid form for use as a box-shaped insulation sheet.